How to Understand Normality, Molarity and Equivalent Weight

Table of Content

• Introduction and outcome
• Normality, Molarity and Equivalent weight
• Equivalent weight
• Molarity
• Normality
• Normality vs molarity case study
• How to convert Normality into Molarity
• Conclusion
• FAQs

Introduction and outcome

Normality, Molarity and Equivalent weight are the most commonly used terms in pharmaceutical analysis to show solute concentration in the solution. Normality and Molarity are used for volumetric solutions while performing the titration and to define buffer concentration during HPLC analysis. In this article, I will share skill-based knowledge and after reading your your knowledge will be enhanced to the next level.

Normality, Molarity and Equivalent weight

Equivalent weight

The Equivalent weight of a substance is the mass of the substance that will combine or displace a fixed quantity of another substance. It is calculated by the following formula:

Equivalent weight = Molecular weight/valency

Typical examples:

Molarity

Molarity is the measure of concentration that is equal to the molecular weight of compound per litre or per 1000 ml of solution.

In other words, when one molecular weight of the compound is dissolved in 1000 ml of any solvent then it becomes 1 molar solution. It is denoted by M. Its unit is moles/L

Case study: Preparation of 1M Sodium hydroxide.

Molecular weight of Sodium hydroxide is 40g/ml. Hence, 1 M will be prepared by dissolving 40 gram Sodium hydroxide in 1000 ml of water.

Normality

Normality is the measure of concentration that is equal to the gram-equivalent weight of compound per litre or per 1000 ml of solution.

In other words, when one equivalent weight of the compound is dissolved in 1000 ml in any solvent, it becomes 1 Normal solution. It is denoted by N. Its unit is Eq/L

Case study: 1N Sulfuric acid solution preparation. Hence, 1 N Sulfuric acid solution will be prepared by dissolving 49.04 gram Sulfuric acid solution in 1000 ml of water.

The Molecular weight of Sulfuric acid is 98.079 g/Eq and hence equivalent weight will be 98.079/2 = 49

Normality vs Molarity Case Study

HCl: 1 M HCl means 1M Hydrogen ions and 1M Chloride ions in the solution. 1 N HCl means 1N hydrogen ion and 1N chloride ion in the solution. Therefore for HCl; 1 M HCl is equal to 1N HCl.

H₂SO₄: 1M of H₂SO₄ gives 2M of Hydrogen ions in the solution. Therefor normality of Hydrogen ions will be 2N for H₂SO₄.

How to Convert Normality into Molarity

The following is the relationship between Normality and Molarity

Normality = Molarity x number of equivalent

Conclusion

Normality, Molarity and Equivalent weights are integral part of pharmaceuticals analysis to represent concentration of analyte in the solution. I hope that now all your doubts related to these terms have cleared. Write your learning and suggestions in the comment section.

FAQs

What do you mean by normality?

When one equivalent weight of compound is dissolved in 1000 ml of water it becomes 1N solution.

How to calculate normality?

The following is the relationship between Normality and Molarity

Normality = Molarity x number of equivalent

What is difference between normality and molarity?

Normality is the measure of concentration that is equal to the gram-equivalent weight of compound per litre or per 1000 ml of solution whereas Molarity is the measure of concentration that is equal to the molecular weight of compound per litre or per 1000 ml of solution.

What is the equivalent weight?

The Equivalent weight of a substance is the mass of the substance that will combine or displace a fixed quantity of another substance.

References

• Advanced Practical Inorganic Chemistry; Dr Y. Thakur and Dr J. Thakur
• Analytical & Industrial Chemistry; Arun, Vijay and Surendra

Abbreviations

• ml: Milliliters
• gm: Gram
• Eq: Equivalent
• L: litre
• HPLC: High-performance liquid chromatography